Flarestacks

ABSTRACT

A flare stack burner tip using the Coanda effect, the bore of the Coanda body is used as a feed line for high pressure gas and the Coanda director surface is positioned across the outlet of the high pressure gas line so as to cause entrainment of air into the fuel gas stream. The feature of the invention is a self adjusting slot between the Coanda surface and gas inlet which adjusts itself automatically to the flow rate of high pressure gas so that a substantially constant pressure is maintained.

[451 Sept. 3, 1974 United States Patent 1 Desty et al.

239/DIG. 7 431/284 Reba et al............ Schreter et al. Hawkes et al.

N 78 2 6677 9999 llll 5220 111 Primary Examiner-Carroll B. Dority, Jr.

Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine Limited,London, England Apr. 18, 1972 [22] Filed:

[2l] Appl. No.: 245,223

ABSTRACT Foreign Application Priority Data Apr. 29, 1971 A flare stackburner tip using the Coanda effect, the bore of the Coanda body is usedas a feed line for high Great Britain 12069/71 pressure gas and theCoanda director surface is positioned across the outlet of the highpressure gas line so as to cause entrainment of air into the fuelgasstream. The feature of the invention is a self adjusting slot betweenthe Coanda surface and gas inlet which adjusts itself automatically tothe flow rate of high pressure wm 1 ,7 M 1 21 a /7 H36 1 vaO 3/ "5 w m 54 2 W O 8 5 UO 4 m w m m3 m m mu m mh m mfi u 6 "e m mM l C um S ud U IFgas so that a substantially constant pressure is maintained.

[56] References Cited UNITED STATES PATENTS 1,628,823 5/1927 Chester et239/506 5 Claims, 6 Drawing Figures liil I.

PAIENTEUSEP 31974 SHEET 10? 4 PATENTEDSEP 31924 3%3337 sneer 3dr 4FLARESTACKS' This invention relates to a burner for disposing of wastecombustible gas, and in particular it relates to the disposal of wastepetroleum gas.

There are many occasions when the oil industry has to handle a crudepetroleum or fraction thereof which has an unacceptably high vapourpressure by reason of the concentration of low molecular weighthydrocarbons, e.g., methane, ethane, propane and butane. It is commonpractice to reduce the vapour pressure by reducing the concentration ofthe volatile components and the combustible gas so produced usually hasa pressure below 6 kN/m (The pressures represent excess overatmospheric).

It is not always possible to sell or otherwise make use of combustiblegases at low pressure and on occasions they have to be sent to waste.This often gives rise to smoky flames, particularly with butane atpressures below 1.5 kN/m Our copending U.S. patent application Ser. No.78,479, now US. Pat. No. 3,709,654 and Ser. No. 245,369, filed Apr. 19,1972 disclose burners for disposing of low pressure waste gasescomprising an inlet adapted to direct a high pressure gas to flow over adirector surface which is curved to initiate flow of gas and air towardsa fuel inlet which is adapted to supply fuel (originally at lowpressure) into the flow of high pressure gas and air. The director bodyis known as a Coanda body and the director surface as a Coanda surface.

Such burners are very useful in situations where the volume of gas to beburned does not fluctuate over wide limits. However, in many operations,flarestacks require a wide turn down range to allow for varyingoperating conditions.

The term turndown range is the ratio of the maximum achievable heatinput to the burner without loss of combustion divided by the minimumheat input thereto.

The low throughput limit of a Coanda flare with a fixed slot occurs atabout 70 kN/m and so, normally, turn down is obtained by using a highmaximum pressure (say 550-650 kN/m giving a turn down of about 3:1).However, high maximum operating pressures have two disadvantagessometimes the gas is not available at sufficient pressure to give thenecessary turn down, and also the noise from the flare increases withthe applied pressure.

We have now discovered that the presence of a self adjusting slotenables the operating pressure to be kept constant or nearly so over awide range of flows, thus giving a wider turn down than normallypossible, and also doing away with the difficulties associated with highpressure operation.

Thus according to the present invention there is provided a flarestackburner tip comprising a feed line for a high pressure gas and a Coandabody as hereinbefore defined having a Coanda surface as hereinbeforedefined positioned across the outlet of the high pressure gas line thecurved director surface Of the Coanda body initiating flow of gas andair along the surface of the Coanda body, there being a self-adjustingslot between the Coanda surface and the high pressure gas line.

By self adjusting slot we mean a slot which adjusts itself automaticallyto the flow rate of high pressure gas so that the pressure of the highpressure gas remains approximately constant on the emerging from theslot.

The high pressure gas may be a fuel gas or it may be steam. Preferablyit emerges from the feed line at a pressure in the range to 300 kN/m Ifthe high pressure gas is fuel gas then preferably the Coanda bodyincludes an internal passage adapted to supply fuel gas at a lowpressure into the flow of high pressure gas and air.

If the high pressure gas is steam then the Coanda body must contain sucha passageway.

According to one aspect of the present invention the Coanda body isallowed to float on the gas stream, as in an air bearing. Theslot willthen open up to pass any required flow at constant pressure. However,this system only allows low operating pressures unless the body isballasted to a high all up weight.

According to another aspect of the invention an external load acts onthe Coanda body through a mechanical advantage inserted between the loadand the Coanda body, thus allowing the load necessary to be reduced bythe appropriate ratio. The connection may be hydraulic, pneumatic ormechanical. This has the double advantage of removing the dead weightfrom the top of the flarestack and reducing theload required. In thecase of remote hydraulic or pneumatic control, the pressure/flowcharacteristics of the flare could be altered as required.

According to a further aspect of the present invention the load on theCoanda body may be increased by fitting a spring which urges the Coandasurface against the high pressure gas inlet. The properties of thespring must be such that the Coanda surface is lifted off the inlet toform the slot when high pressure fuel gas or steam is introduced.

Although the use of a spring loaded system rather than a free floatingone means that the pressure is no longer constant for all flows, theflow increases as the square of the pressure, giving a very steepcharacteristic and good turn down. v,

All the above involve movement of the flare tip, with a consequentrequirement for suitable guides and flexible connections in the case ofa central low pressure feed.

According to a still further aspect'of the present invention theadjustable slot is provided by fitting a bellows joint in the feed pipejust below the slot. This allows gas adjustment to be made simplywithout movement of the tip itself, since the pressure on the lip of theslot can be made to open this slot to the required width.

Preferably springs are used in parallel with the bellows. This use ofadditional springs is a convenient way of obtaining the required slotclosure pressure for a particular application and has the advantagesthat i. The bellows are working at lower stress levels making possible alonger working life.

ii. Manufacturing variations in the bellows can be allowed for bysuitable choice of spring strength. in. The same bellows can be used forflares of different specification by appropriate springselection.

It is known that a stream of gas will stick" to a suitably shapedsurface and a curved surface can deflecta stream of gas and therebyproduce a low pressure zone. In the burner according to the invention,the initial portion of the director surface is the surface of revolutionformed by the rotation of a quadrant of a circle about the longitudinalaxis of the Coanda body, the curved section of the quadrant beingtangential to the slot. This produces a zone of low pressure into whichsurrounding atmospheric air flows.

During the use of the burner, the low pressure zone contains gas withhigh kinetic energy. In order to improve the flow pattern away from thelow pressure zone, the final portion of the director body is shaped soas to reduce the kinetic energy and increase the pressure of the gas,e.g., the final portion of the director body is tapered.

The invention also includesa method for disposing of waste combustiblegas by use of a flarestack burner tip as hereinbefore described.

The invention is illustrated with reference to FIGS. 1 4 of the drawingaccompanying the provisional specification and FIG. of the completespecification.

OF THE DRAWINGS:

FIG. 1 is a fragmentary vertical sectional view, partly in elevation, ofa flarestack burner tip constructed in accordance with the invention,illustrating the Coanda body portion thereof in a free floating positionover a high pressure fuel gas outlet to provide a fuel gas outlet slotthat is self-adjustable according to the flow rate of the gas;

FIG. 2 is a viewsimilar to that of FIG. 1, illustrating a firstalternative embodiment of a flarestack burner tip constructed inaccordance with the invention, the view illustrating a hydraulic systemfor applying an add'itional load to the Coanda body portion of theburner p;

FIG. 3 is a view similar to FIG. 1, illustrating a second alternativeembodiment of a flarestack burner tip constructed in accordance with theinvention, the view illustrating a spring member applying an additionalload to the Coanda body portion of the burner tip;

FIG. 4 is a vertical sectional view, partly in elevation, of a thirdalternative embodiment of a flarestack burner constructed in accordancewith the invention, illustrating the Coanda body portion of the burnermounted in a fixed position while a bellows section provided in the gasoutlet line permits the gas outlet slot to be self-adjustable responsiveto the gas flow-rate;

FIG. 5 is a fragmentary view in side elevation of a fourth alternativeembodiment of a flarestack burner tip constructed in accordance with theinvention illustrating a fuel gas line containing both a bellows sectionproviding self-regulation of the gas outlet slot and a plurality ofsprings for assisting movement of the bellows; and l FIG. 6 is avertical sectional view, partly in elevation, of a fifth alternativeembodiment of a flarestack burner tip constructed in accordance with theinvention, illustrating a fixed Coanda body portion and a high pressuregas line containing a bellows section, all similarly to that shown inFIG. 4, and including a low pressure fuel gas line extending through theCoanda body.

The flarestack tip comprises a Coanda bodyl and a line 2 for the supplyof high pressure fuel gas. When gas is flowing, a slot 3 opens upbetween the body 1 and the line 2.

The body 1 has a director surface comprising two portions 4 and 5 whichmerge into one another. 4 is a deflector portion which turns thedirection of the high pressure gas from horizontal to vertical and 5 isa tapered portion which modifies the flow between the deflector portion4 and the top of the body 1.

The shape of the deflector portion 4 is most conveniently specified asthe surface of revolution formed by the rotation of a quadrant of acircle about the longitudinal axis of the Coanda body, the curvedsection of the quadrant being tangential to the slot; as shown in thedrawings the distance between the axis of rotation and the centre of thequadrant is equal of the radius of the quadrant. The shape of thetapered portion 5 is that of a frustum of a cone.

As the high pressure fuel gas flows round the deflector portion 4 itsdirection of flow is changed from (initially) horizontal to vertical.This induces a low pressure zone in the surrounding air and hence itinduces movement of air as well as fuel towards the top of the body 1.

The body 1 is positioned within the line 2 by a guide 6.

In FIG. 1, the body 1 is free floating. At the balance pointPA W, whereP is the pressure of the gas in the seat pipe, A is the cross section ofthe pipe and W is the weight of the body 1.

Hence, since A and Ware constant, P is constant and regardless of thegas flow, the gap merely opens to accomodate it. i

In FIG. 2, additional loading is applied to the body 1 by means of ahydraulic system.

A load 10 is applied to the piston 11 of a narrow hydraulic cylinder 12.The body 1 is connected to the piston 13 of a wide hydraulic cylinder14. A line 15 transfers hydraulic pressure between the cylinders 12 and14.

In this case the mechanical advantage of the hydraulic system W W A /Awherein W, is the weight of the applied load 10, W is the weight of thebody 1, A is the area of the cylinder 12 and A is the area of thecylinder 14.

With reference to FIG. 3, a spring 20 urges the body 1 towards the line2 and opposes the lifting action of the high pressure gas.

At equilibrium, W, A P Rd, wherein W is the weight of the body 1, A isthe area of the line 2, P is the pressure in the line 2, R is the springrate and d is the spring deflection.

With reference to FIG. 4, the line 2 contains a spring bellows section30 just below its outlet. If the pressure of emerging gas increases,then the slot 3 widens, i.e., relative motion between the body 1 and theline 2 takes place. However, in the embodiments described with referenceto FIGS. 1-3, it is the body which has moved and the line which hasremained fixed. In the FIG. 4 embodiment, the body remains fixed, almostall of the line 2 remains fixed and the relative motion is accomodatedby contraction of the bellows 30. Conversely, a diminution of pressureresults in an expansion of the bellows. Using this method, the diameterof the outer tube 2 at the gas exit slot 3 must exceed the diameter ofthe bellows 30 so the force due to the gas pressure on the slot-3exceeds the force opening the bellows 30 by internal pressure.-

At equilibrium, A P R d wherein AK, is the neteffective area, P is thepressure of the gas in the line 2, R is the spring rate of the springbellows and d is the deflection.

With reference to FIG. 5, additional springs 40 assist the bellows 30 inits slot closure action. They act in parallel with the bellows 30 andare attached to the line 2 above and below the bellows 30. Byappropriate adjustment of the strength of the springs 40, variations inflare specification and bellows manufacture may be allowed for. Thelarge screws 16 allow spring compression and adjustment.

Referring now to FIG. 6 of the accompanying drawings, there isillustrated a fixed Coanda body 1 and a high pressure gas line 2containing a bellows section 30, all in a similar manner to that shownin the embodiment illustrated in FIG. 4, and including a low pressurefuel gas conduit line 50 extending internally through the Coanda body 1.It will be understood from the preceding discussion that a low pressurefuel gas flowing through the internal conduit 50 exits at 51 to besubsequently mixed with the flow of high pressure gas and entrainedatmospheric air exiting from the Coanda body for combustion.

What we claim is:

l. A flarestack burner tip, comprising:

a high pressure gas conduit line terminating in a generally verticalportion;

a Coanda body positioned over the upper end of said high pressure gasconduit line, said Coanda body having an external deflector surfacepositioned adjacent to and extending completely across the upper end ofsaid high pressure gas conduit line,

said deflector surface including a substantially horizontal portionadapted to form a circumferentially extending slot with the upper end ofsaid high pressure gas conduit upon said Coanda body being spacedtherefrom and a curved portion extending outwardly from said highpressure gas conduit line and tangentially to said horizontal portion,said slot adapted to direct high pressure gas over said curved portionof said Coanda deflector surface; and

wherein said Coanda body is fixedly mounted with respect to said highpressure gas conduit line and the latter includes a flexible bellowssection pemitting the upper end of said high pressure gas conduit lineto freely move toward and away from said Coanda body responsive to thepressure of the flow of said high pressure gas to thereby maintain asubstantially constant pressure on the gas passing through said slot.

2. A flarestack burner tip, comprising:

a high pressure gas conduit line tenninating in a generally verticalportion; a Coanda body positioned over the upper end of said highpressure gas conduit line, said Coanda body having an external deflectorsurface positioned adjacent to and extending completely across the upperend of said high pressure gas conduit line, said deflector surfaceincluding a substantially horizontal portion adapted to form acircumferen tially extending slot with the upper end of said highpressure gas conduit upon said Coanda body being spaced therefrom, acurved portion extending outwardly from said high pressure gas conduitline and tangentially to said horizontal portion, and terminating in atapered portion extending in a general vertical direction tangentiallyto said curved deflector surface portion, said slot adapted to directhigh pressure gas over said curved portion of said Coanda deflectorsurface; said Coanda body further including a low pressure fuel gasconduit line extending internally through said Coanda body adapted tosupply a low pressure fuel gas into the flow of high pressure fuel gasand entrained atmospheric air from the external surface of said Coandabody; and

means mounting said Coanda body for free vertical movement with respectto the upper end of said high pressure gas conduit line responsive tothe pressure of the flow of said high pressure gas to thereby maintain asubstantially constant pressure on the gas passing through the slot.

3. A flarestack burner tip as claimed in claim 1, wherein said curvedportion of said Coanda deflector surface comprises a surface ofrevolution formed by the rotation of a quadrant of a circle about thelongitudinal axis of the Coanda body.

4. A flarestack burner tip as claimed in claim 1,

sure gas conduit line. I

$22233? UNITED ST T aom fi, CERTIFICATE OF CORRECTIQN 5 m 3,833,337 3 aSeptember 3,1974

Inventor) Denis Henry Desty and Christopher John Young It is certifiedthat error appears in the aboire-identified patent and that saidLetters. Patent are hereby corrected as shown below:

1 Column 2, line 48, change "gas" to gap Signed and sealed this 17th dayDecember-1974.

(SEAL) Attest: I

McC-OY M. GIBSON JR. 0. MARSHALL DANN Attesting Officer Cqmnissioner ofPatents

1. A flarestack burner tip, comprising: a high pressure gas conduit lineterminating in a generally vertical portion; a Coanda body positionedover the upper end of said high pressure gas conduit Line, said Coandabody having an external deflector surface positioned adjacent to andextending completely across the upper end of said high pressure gasconduit line, said deflector surface including a substantiallyhorizontal portion adapted to form a circumferentially extending slotwith the upper end of said high pressure gas conduit upon said Coandabody being spaced therefrom and a curved portion extending outwardlyfrom said high pressure gas conduit line and tangentially to saidhorizontal portion, said slot adapted to direct high pressure gas oversaid curved portion of said Coanda deflector surface; and wherein saidCoanda body is fixedly mounted with respect to said high pressure gasconduit line and the latter includes a flexible bellows sectionpemitting the upper end of said high pressure gas conduit line to freelymove toward and away from said Coanda body responsive to the pressure ofthe flow of said high pressure gas to thereby maintain a substantiallyconstant pressure on the gas passing through said slot.
 2. A flarestackburner tip, comprising: a high pressure gas conduit line terminating ina generally vertical portion; a Coanda body positioned over the upperend of said high pressure gas conduit line, said Coanda body having anexternal deflector surface positioned adjacent to and extendingcompletely across the upper end of said high pressure gas conduit line,said deflector surface including a substantially horizontal portionadapted to form a circumferentially extending slot with the upper end ofsaid high pressure gas conduit upon said Coanda body being spacedtherefrom, a curved portion extending outwardly from said high pressuregas conduit line and tangentially to said horizontal portion, andterminating in a tapered portion extending in a general verticaldirection tangentially to said curved deflector surface portion, saidslot adapted to direct high pressure gas over said curved portion ofsaid Coanda deflector surface; said Coanda body further including a lowpressure fuel gas conduit line extending internally through said Coandabody adapted to supply a low pressure fuel gas into the flow of highpressure fuel gas and entrained atmospheric air from the externalsurface of said Coanda body; and means mounting said Coanda body forfree vertical movement with respect to the upper end of said highpressure gas conduit line responsive to the pressure of the flow of saidhigh pressure gas to thereby maintain a substantially constant pressureon the gas passing through the slot.
 3. A flarestack burner tip asclaimed in claim 1, wherein said curved portion of said Coanda deflectorsurface comprises a surface of revolution formed by the rotation of aquadrant of a circle about the longitudinal axis of the Coanda body. 4.A flarestack burner tip as claimed in claim 1, wherein said Coanda bodyincludes a generally centrally disposed spindle member extendingdownwardly from said horizontal portion of said deflector surface intotelescoping freely slidable movement with guide means fixedly mountedwithin said high pressure gas conduit line.
 5. A flarestack burner tipas claimed in claim 1, including spring means adapted to provide anexternal load to said flexible bellows section of said high pressure gasconduit line.